Roy's model of nursing sees an individual as a set of interrelated systems, biological, psychological, and social. The individual tries to maintain a balance between each of these systems and the outside world. However, there is no absolute level of balance. According to Roy we all strive to live within a band where we can cope adequately. This band will be unique to an individual. The adaptation level is the range of adaptability within which they can deal effectively with new experiences.

Roy maintains that there are four main adaptation systems which she calls modes of adaptation. She calls these the physiological system, the self concept system, the role mastery system and the interdependency system.